Roof Black Ship Rats

Introduction:

The roof rat (Rattus rattus, Fig. 1) is one of two introduced rats found in the contiguous 48 states. The Norway rat (R. norvegicus) is the other species and is better known because of its widespread distribution. A third rat species, the Polynesian rat (R. exulans) is present in the Hawaiian Islands but not on the mainland. Rattus rattus is commonly known as the roof rat, black rat, and ship rat. Roof rats were common on early sailing ships and apparently arrived in North America by that route. This rat has a long history as a carrier of plague.

Distribution

The black rat originated in India and Southeast Asia, and spread to the Near East and Egypt, and then throughout the Roman Empire, reaching Great Britain as early as the 1st century.[11] Europeans subsequently spread it throughout the world. The black rat is again largely confined to warmer areas, having been supplanted by the brown rat (Rattus norvegicus) in cooler regions and urban areas. In addition to being larger and more aggressive, the change from wooden structures and thatched roofs to bricked and tiled buildings favored the burrowing brown rats over the arboreal black rats. In addition, brown rats eat a wider variety of foods, and are more resistant to weather extremes.

Black rat populations can explode under certain circumstances, perhaps having to do with the timing of the fruiting of the bamboo plant, and cause devastation to the plantings of subsistence farmers; this phenomenon is known as Mautam in parts of India.

Diet

Black rats are considered omnivores and eat a wide range of foods, including seeds, fruit, stems, leaves, fungi, and a variety of invertebrates and vertebrates. They are generalists, and thus not very specific in their food preferences, which is indicated by their tendency to feed on any meal provided for cows, swine, chickens, cats, and dogs.They are similar to the tree squirrel in their preference of fruits and nuts. They eat about 15 grams (0.53 oz) per day and drink about 15 millilitres (0.53 imp fl oz; 0.51 US fl oz) per day. Their diet is high in water content. They are a threat to many natural habitats because they feed on birds and insects. They are also a threat to many farmers since they feed on a variety of agricultural-based crops, such as cereals, sugar cane, coconuts, cocoa, oranges, and coffee beans.

Nesting behavior

Through the usage of tracking devices such as radio transmitters, rats have been found to occupy dens located in trees, as well as on the ground. In Puketi, a forest in Kauri, New Zealand, rats have been found to form dens together. Rats appear to den and forage in separate areas in their home range depending on the availability of food resources.Research shows that in New South Wales, the black rat prefers to inhabit lower leaf litter of forest habitat. There is also an apparent correlation between the canopy height and logs and the presence of black rats. This correlation may be a result of the distribution of the abundance of prey as well as available refuges for rats to avoid predators. As found in North Head, New South Wales, there is positive correlation between rat abundance, leaf litter cover, canopy height, and litter depth. All other habitat variables showed little to no correlation. While this species' relative, the brown (Norway) rat prefers to nest near the ground of a building the black rat will prefer the upper floors and roof. Because of this habit they have been given the common name roof rat.

Foraging behavior

As generalists, black rats express great flexibility in their foraging behavior. They are predatory animals and adapt to different micro-habitats. They often meet and forage together in close proximity within and between sexes.Rats tend to forage after sunset. If the food cannot be eaten quickly, they will search for a place to carry and hoard to eat at a later time.Although black rats eat a broad range of foods, they are highly selective feeders; only a restricted number of the foods they eat are dominant foods.When black rat populations are presented with a wide diversity of foods, they eat only a small sample of each of the available foods. This allows them to monitor the quality of foods that are present year round, such as leaves, as well as seasonal foods, such as herbs and insects. This method of operating on a set of foraging standards ultimately determines the final composition of their meals. Also, by sampling the available food in an area, the rats maintain a dynamic food supply, balance their nutrient intake, and avoid intoxication by secondary compounds.

Predators and diseases

The black rat serves as prey to cats and owls in domestic settings. In less urban settings, rats are preyed upon by weasels, foxes, and coyotes. These predators have little effect on the control of the black rat population because black rats are agile and fast climbers. In addition to agility, the black rat also makes use of its keen sense of hearing to detect danger and quickly evade mammalian and avian predators.Rats serve as outstanding vectors for transmittance of diseases because they have the ability to carry bacteria and viruses in their systems. There are a number of bacterial diseases that are common to rats, and these include Streptococcus pneumoniae, Corynebacterium kutsheri, Bacillus piliformis, Pasteurella pneumotropica, and Streptobacillus moniliformis, to name a few. All of these bacteria are disease causing agents in humans. In some cases, these diseases are incurable.

Management

Large-scale rat control programs have been taken to maintain a steady level of the invasive predators in order to conserve the native species in New Zealand such as kokako and mohua.Pesticides, such as pindone and 1080 (sodium fluoroacetate), are commonly distributed via aerial spray by helicopter as a method of mass control on islands infested with invasive rat populations. Bait, such as brodifacoum, is also used along with coloured dyes in order to kill and identify rats for experimental and tracking purposes. Another method to track rats is the use of wired cage traps, which are used along with bait, such as rolled oats and peanut butter, to tag and track rats to determine population sizes through methods like mark-recapture and radio-tracking.Poison control methods are effective in reducing rat populations to nonthreatening sizes, but rat populations often rebound to normal size within months. Besides their highly adaptive foraging behavior and fast reproduction, the exact mechanisms for their rebound is unclear and are still being studied.